Means for controlling sensitivity of voice operated devices



July '14, 1931. s. B. WRIGHT ETAL l 1,814,018

MEANS FOk--CONTROLLLNG SENSITIVITY OF VOICE OPERATED DEVICES Filed June e. 1928 ff f1 l f .lulu

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ATTORN EY sum E. WRIGHT, or soU'rH ORANGE, NEW NEW Yonx, N. Y., AssIGNoEs To AMERICAN Patented July 14, 1931 UNITED STATES PATENT oFFlcE PANY, A CORPORATION OF N EW YORK MEANS FOR CONTROLLING SENSITIVITY OF VOICE OPLERATED DEVICES .Application filed June 6, 1928. Serial No. 283,407.

This invention relates to improvements in voice operated devices, and more particularly to arrangements for automatically regulating the sensitivity of such devices: An echo suppressor is such a voice operated device well known in the art and is utilized in connection with a two-way transmission system for disabling one of the oneway lines of such system, while transmission is taking place in the opposite direction over another of the one-way lines of the system, thereby preventing echo effects orreflected currents from bein transmitted back to the transmitting end o the system and causing a disturbance or singing. The disabling apparatus usually comprises a short circuit which may be closed 'across'the one-way line by the operation of a voice operated relay device connected to the one-way line for transmission in the o posite direction. Y

The voice operated) echo suppressor must be so constructed that it will not be operated by noise currents existing on the system. Accordingly, it has been the practice to limit the sensitivity of the device by the greatest noise ever expectedto be present on the line.V

VAs Ythe line would `not at'all times include this maximum noise current, it is obvious that' during quiet periods, the voice operated echo suppressor device would not be operating at maximum eiliciency. It is the primary object of the invention to automaticall vary the sensitivity of a voice operated dlavice, such as the echo suppressor, in accordance with the volume of noise on the line so that on quiet connectionsits sensitivity will not be limited by the Vmaximum noise to be expected. The arrangements of the invention for automaticallyy regulating the sensitivity of a device are applicable to voice operated systems, four-wire echo suppress'ors, two-wire echo Suppressors, and anti- Vsinging devices, among others. Other objects and features of the invention will appear more fully from the detailed description thereof hereinafter given. The invention may be more fully understood from the followingl description tother with the accompanying drawing, in t e figure of which is shown a circuit diagram illustrating a preferred embodiment of the invention.

In the drawing, the invention is illustrated in connection with a voice operated echo suppressor device connected between the. oneway lines of a circuitof t-he Well-known four-wire type. The invention has been illustrated in connection with such an Vecho suppressor as this is believed to be a practical desirable use of the invention. Two one-way line sections for transmission in opposite directions -are shown as L1 and L2. Bridged across line Ll is a circuit 3 including a device comprising the vacuum tubes 5, 6 and 7 and the echo suppressor relay 8, which controls a short circuit across line L2. Bridged across line L2 is a circuit 4 including a device comprising the vacuum tubes'9, l0 and 1l and the echo suppressor relay 12 which controls a short circuit across line L1. Ampliiiers l and 2 are shown in the lines L1 and L2. The general operating features art.

An echo suppressor without the automatic regulating features, of this invention would normally have the sensitivity of its voice operated relays 8 and lQ'limited bythe maximum amount of noise current to be expected over lines L1 and L2. It is known that the amounts of noise on different circuits vary over a Wide range, the difierence between extreme conditions being at least 30 TU. Accordingly, it will be seen that it might be permissible to set echo suppressors 3Q TU more sensitive than heretofore if the arrangements of this invention are provided to automatically reduce their sensitivity to take care of variations in noise. In `accordance with this invention, the voice operated devices may beset at maximum sensitivity. Automatically operating control apparatus is provided to slowly reduce the sensitivity of both voice operated devices when either one is affected by steady noise but to quickly restore maximum sensitivity when this steady noise is not present. In other. words, the arrangements of the invention will slowly reduce the sensitivity of 'the voice operated device and hold it to a JERSEY, AND noEEN MITCHELL, 0E TELEPHONE AND TELEGEAEHCOM- f of an echo suppressorV are well known in the given 'value suitable for preventing operation by a continuous steady volume within the range of noise currents, and quickly increase sensitivity to a higher value when this steady volume has ceased. Arrangements are provided whereby both voice operated echo suppressor devices are acted upon in order to obviate the possibility ot alseoperation. rihus, it the sensitivity of one Vsuppressor only were reduced, transmission which was too weak to operate that suppressor might be strong enough as an echo to operate the other suppressor due to the difference in sensitivities.

The control apparatus illustrated is a vacuum tube device having a threshold action and comprising the tubes 5, 6 and 7. The circuit 8 bridged across the line L1 is connected to theinput of tube 5, which although an amplii'ier, is biased like a rectiiier. It is normally biased by the drop in resistance 14 and the battery 13 to respond to the upper halt oi the impressed wave only. The output then passes through a transformer to the detector tube 6. The output of the detector tube 6 is connected to the echo suppressor relay 8 which ccntrols a short circuit across circuit 4 and line L2. The output current from tube 6 by passing through resistance 15 produces a voltage drop in said resistance and impresses, through transformer 16, an -alternating voltage wave on the grid of tube 7 through the resistance 17 and the condenser in parallel. A charge is stored up in the condenser in the well-known manner yand produces a negative potential on the grid of the tube 7, thus causing its plate current to decrease. The action of the current from the output of tube 6 will thus tend to decrease the plate current of tube 7. in

`other words, when an alternating wave is impressed on the grid of tube 7, during the positive half of the wave current may flow from the grid to the lilament and `through resistance 17 and the condenser 30. This resistance is suiiiciently large and the condenser sutliciently small so that the voltage of the grid will not be raised to any effective degree by this current. The resistance 17 and the condenser 30 are so proportioned that the condenser will notbe wholly discharged during the negative halt cycle. During the negative halt ot the impressed wave no current can flow from the filament to the grid, but the potential difference across the condenser is added to the applied voltage .to give a large negative grid voltage. As is well known, the increase of the negative potential on the grid will tend to decrease the plate current. In other words, any increase in the output current of the rectifier tube 6 will tend to decrease the current flow in the plate circuit of tube 7. In the plate circuit of tube 7 are the battery 18, condensers 19 and 20 and resistance elements 22 and 14. Resistance 14 will be of a relatively high value. The eect of a reduction of the current in the plate circuit of tube 7 by alternating current impulses coming in from the output of tube 6 will be to cause condensers 19 and 2O to discharge. These condensers must discharge through'the high resistances 14, 421 and 22 and hence will discharge slowly.Y If the plate current of tube 7 is increased,due to a lessening in the incoming impulses, the condensers `will rapidly charge up. Accordingly, the combination of the output resistance of tube 7, the condensers 19 and 20, and resistances 14 and 22 will form a tast operate slow release circuit which is normally in the operated condition. Accordingly, a decrease in the plate current of tube 7 will slowly increase the negative bias on the grid ot the amplifier .tube 5 and render it less etiective, but an increase in the plate current oi tube 7 will rapidly restore the amplifier tube 5 to maximum effectiveness. In other words, the threshold ot operation of the device may be slowly reduced from its maximum, but rapidly restored thereto. Due lto the amplification in tubes 5, 6 and 7, the steady state output of tube 6 may be reduced to a very small traction of its initial value before the slow release circuit has acted.

Connected to circuit 4 is a vacuum tube arrangement comprising the tubes 9, 10' and 11 controlling the echo suppressor relay 12. This arrangement is substantially similar to that already described. yIn order that noise currents coming in over one lof the lines may affect both of theecho suppressor devices, the .circuit 23 is prov-ided-con- :l necting the input of tube 7 with the input of a similar tube 11 in the other device. The value of resistance 17 and the corresponding resistance in the other device would 'be large enough toprevent any slight action of one control circuit on the plate .,ciri cuit of the detector tube in the other circuit.

While the invention has beendisclosed as embodied in certain specific arrangements which are deemed desirable, it is4 Vunderstood that it is capable of embodiment in many and other widely varied'forms without departing from the spirit of the invention as dened by the appended claims.

W'hat is claimed is:

1. A transmission line, an echo suppressor device associatedtherewith, anda device in said line for controlling the operation of said echo suppressor device, said control device comprising a vacuum tubearrangement having the threshold of operation .affected solely in proportion to the amount Vof input current applied thereto in a kcomparatively steady stat-e.

'2. A transmission line, an echo suppressor device associated therewith, and a device in said line for controlling the operation of said echo suppressor device, said control device comprising an ampliier tube, a detector tube associating said amplier tube with said echo suppressor device, and a third tube connecting the output of said detector with the said amplifier whereby an increase in comparatively steady current in said detectory output will decrease the effectiveness of said amplifier tube.

3. A transmission line, an echo suppressor device associated therewith and a device in said line for controlling the sensitivity of said echo suppressor device, said control device comprising an amplifier tube associated with said line and arranged to'operate at maximum sensitivity, a detector tube associating said amplifier tube with said echo suppressor devlce, a third tube connecting the output of said detector withY said amplifier whereby the effectiveness Aof said amplifier may be controlled by the current in said detector output, and electrical delay means in the output of said third tube.

In testimony whereof, We have signed our names to this specification this 5th day of June, 1928.

SUMN ER B. WRIGHT. DOREN MITCHELL. 

